Evolution and taxonomy in the genus Brucella: progesterone induction of filterable forms of Brucella abortus type 2 with revertant characteristics essentially indistinguishable in vitro from those of Brucella ovis.

An organism essentially indistinguishable from Brucella ovis, as determined by conventional and manometric techniques of identifying Brucella organisms, was derived in vitro from a strain of Brucella abortus type 2. The basic mechanism responsible for derivation of this organism was incomplete reversion of the L-forms to their original parental characteristics. The agent used to induce the L-forms was a physiologic concentration of progesterone incorporated in the growth medium.